adopted of controlling it at the burner, the construction of a good Argand was, under the circumstances, almost impossible. The batswing was not so prejudicially affected by an excess of pressure. Pressure to some extent was, indeed, required to enable the flame to attain its normal shape; while any excess forced the gas through the flame without permitting it to be raised to incandescence before being consumed, and although necessitating loss of light, caused no inconvenience like a smoking flame. Another important advantage which the batswing possessed over the Argand burner was its simplicity of construction; and the absence of accessories, such as the glass chimney—dispensing with the cleaning and attention which the latter required. Had the benefits of gas lighting been dependent upon the use of apparatus so fragile, and requiring so much care and attention as the Argand, the range of its applicability must have been considerably limited, and its prospects of commercial success much less assured. The introduction of a series of cheap but effective burners, however, altered the conditions of gas lighting, and marked the commencement of a new era in artificial illumination. The possibility of obtaining, by means of a burner so simple and apparently insignificant as the batswing, results little, if at all, inferior to what could be obtained by the use of the most complicated and expensive, was of advantage alike to the consumer and the producer of gas. To the former it gave the benefits of an increased illumination, without requiring any corresponding outlay; to the latter it promised a growing extension of the use of coal gas, and thus furnished the surest guarantee of future progress and prosperity.

THE UNION-JET, OR FISHTAIL BURNER.

The batswing had been for some years in extensive use before a burner was produced worthy in any degree to compare with it in respect to simplicity and efficiency. The invention of the union-jet, or fishtail burner, furnished a competitor equally simple; little, if at all, inferior as regards efficiency; and, to some extent, superior to the former burner in general adaptability. Although so much behind in point of time, the new burner speedily rivalled the older batswing in popular favour; and in its various modifications and improvements may be said, without fear of contradiction, to have received a wider application than any other gas-burner. As in the case of the batswing, so with regard to this burner: few details are recorded of its invention. But, slight as is the information available, such as we have is more satisfactory and more authentic than the meagre notice of Clegg, which is all that is known of the invention of the former burner. It appears to be established beyond doubt that the union-jet is the joint Who invented the union-jet burner? invention of Mr. James B. Neilson, the inventor of the hot-blast, and Mr. James Milne, of Glasgow, founder of the engineering firm of Milne and Son. About the year 1820, or soon after (as in that year Mr. Neilson was appointed Manager of the Glasgow Gas-Works), these gentlemen were experimenting with gas-burners, when they discovered that by allowing two jets of gas, of equal size, to impinge upon each other at a certain angle, a flat-flame was produced, with increased light. This was the origin of the union-jet; so called from the manner in which the flame is produced. At first separate nipples were employed for the two jets; but, very soon, Mr. Milne hit upon the expedient of drilling two holes, at the required angle, in the same nipple. In this manner, with slight modifications, the burner has continued to be constructed down to the present day.

Fig. 3.—Fishtail Burner.

The explanation of the preference accorded to this burner over its predecessor, the batswing, is to be found chiefly, I think, in the very different shapes of the respective flames produced by the two burners. The batswing, in its original form, produced a flame of great width, but of no corresponding height. The extremities of the flame, stretching out from the burner so far on either hand, were easily affected by an agitation of, or commotion in the surrounding atmosphere; a slight draught or current of air causing the flame to smoke at these points. The extreme width of flame also precluded the use of this burner in globes. The flame produced by the union-jet burner, as first constructed, was very different to the one just described. Longer than that of the batswing, and considerably narrower (but widening gradually from its base, at the burner, to its apex), it presented somewhat nearly the appearance of an isosceles triangle; or more closely, perhaps (with its slightly-forked apex), the tail of a fish, from which resemblance it is commonly designated the fishtail burner. This form of flame was better adapted for use in globes, and also better withstood the effects of draughts. And it is perhaps not unreasonable to suppose that as in shape it approached more closely to the kind of flame with which the people had been familiar in oil lamps, the flame produced by the union-jet burner was more agreeable to the eye than that of the batswing, and that this seemingly trivial consideration will account, to some extent at least, for the undue favour shown towards it. For it must not be assumed, because of the widespread popularity to which the union-jet so early attained, and which it has continued to enjoy, that it was of necessity a better burner (in the sense of developing more light for the gas consumed) than the one which preceded it. On the contrary, in this regard it was not quite so effective as the batswing. Nor is this result surprising, looking at the different methods adopted in the two burners for producing the same effects of light and flame.

From the batswing burner the gas issued in a thin but widely-extending stream, presenting, when ignited, a continuous sheet of flame; its height and width depending upon the pressure at which the gas was supplied, but always offering an unbroken surface of flame to the air. Although, from the excessive pressures which, in the early days of gas lighting, were generally employed, the flame drew upon its surface too much air for the attainment of the fullest lighting efficiency obtainable from the gas; yet the form given to the issuing stream of Union-jet and batswing burners compared. gas precluded the air from entering the interior of the flame, and still further reducing its illuminating power. With the union-jet burner the conditions were greatly changed; and this latter evil, of the introduction of cold air into the interior of the flame, was one of the consequences entailed by the means it employed for producing its flame. From this burner the gas issued in two narrow streams, like single jets, which, directly after emerging from the burner, impinged upon each other at a given angle; the mutual shock given to the streams of gas when thus arrested causing them to spread out in a lateral direction, and (the high velocity at which the gas issued being expended) to unite, and ascend in a sluggish stream until consumed. That injury to the illuminating power of the flame should result from causes connected with the manner of producing it will be understood on considering some of the phenomena associated with the production of a gas flame.

When a jet or stream of gas issues into a still atmosphere, it produces in its immediate neighbourhood, on all sides, an area of low pressure, to occupy which the contiguous air rushes in. Induced air currents are thus set up in close proximity to, and having the same direction as the issuing stream of gas, and varying in force with the pressure, or velocity, at which the gas issues. The non-luminous flame of the Bunsen burner, and of the so-called